1. Field of the Invention
The present invention relates to an external force judgment method and an external force judgment device of a human-collaborative industrial robot.
2. Description of the Related Art
In the case of a human-collaborative industrial robot working in collaboration with a human worker, the worker and the robot may come close to each other during work and may mistakenly come in contact with each other. If such a contact occurs, immediate detection of the contact and then implements of safety measures such as stop of the robot are needed. A contact between a worker and a robot can be detected by judging the presence or absence of an external force acting on the robot. With this regard, for example, U.S. Laid-open Patent Publication No. 2013/0211739 (US2013/0211739A1) discloses a method for estimating a torque acting on an arm of a robot in which the arm is driven by a motor through a decelerator. Specifically, in US2013/0211739A1, a rotation angle of the motor and a rotation angle of an output shaft of the decelerator, respectively, are detected, and based on a difference between the two rotation angles, the torque is estimated.
However, the torque of a decelerator has characteristics in which it changes nonlinearly with respect to changes in the rotation angles due to backlash, friction, hysteresis, or the like. Accordingly, if a torque is estimated based on a difference between the rotation angle of a motor and the rotation angle of an output shaft of a decelerator, as described in US2013/0211739A1, it is not possible to judge the presence or absence of an external force acting on a robot with high precision.